Comments

From: Oleg Nesterov <oleg@redhat.com>
CVE-2013-0871
BugLink: http://bugs.launchpad.net/bugs/1129192
It is not clear why ptrace_resume() does wake_up_process(). Unless the
caller is PTRACE_KILL the tracee should be TASK_TRACED so we can use
wake_up_state(__TASK_TRACED). If sys_ptrace() races with SIGKILL we do
not need the extra and potentionally spurious wakeup.
If the caller is PTRACE_KILL, wake_up_process() is even more wrong.
The tracee can sleep in any state in any place, and if we have a buggy
code which doesn't handle a spurious wakeup correctly PTRACE_KILL can
be used to exploit it. For example:
int main(void)
{
int child, status;
child = fork();
if (!child) {
int ret;
assert(ptrace(PTRACE_TRACEME, 0,0,0) == 0);
ret = pause();
printf("pause: %d %m\n", ret);
return 0x23;
}
sleep(1);
assert(ptrace(PTRACE_KILL, child, 0,0) == 0);
assert(child == wait(&status));
printf("wait: %x\n", status);
return 0;
}
prints "pause: -1 Unknown error 514", -ERESTARTNOHAND leaks to the
userland. In this case sys_pause() is buggy as well and should be
fixed.
I do not know what was the original rationality behind PTRACE_KILL.
The man page is simply wrong and afaics it was always wrong. Imho
it should be deprecated, or may be it should do send_sig(SIGKILL)
as Denys suggests, but in any case I do not think that the current
behaviour was intentional.
Note: there is another problem, ptrace_resume() changes ->exit_code
and this can race with SIGKILL too. Eventually we should change ptrace
to not use ->exit_code.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
(cherry picked from commit 0666fb51b1483f27506e212cc7f7b2645b5c7acc)
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
kernel/ptrace.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)